This section provides background information related to the present disclosure which is not necessarily prior art.
Various methods are known in the art for joining a plastic workpiece to a further workpiece. For example, DE 3 109 500 A1 discloses such a method, wherein a plastic workpiece having an abutment surface and a projection projecting away from the abutment surface, and a further workpiece having a first surface, a second surface opposite to the first surface, and a through hole which connects the first surface to the second surface are provided. The plastic workpiece and the further workpiece are arranged relative to one another such that the abutment surface of the plastic workpiece abuts on the first surface of the further workpiece and the projection extends through the through hole such that the front surface of the projection exceeds the second surface of the further workpiece.
Subsequently, a rotating friction tool having a rosette shaped working surface and a central spike extending away from said working surface, is moved onto the front surface of the projection, so that the friction between the spike and the projection causes the material of the projection to plasticize and to be displaced to the sides and into the cavities of the rosette shaped working surface, while the friction tool is moved further towards the further workpiece and the spike further penetrates the projection. When the lateral sides of the working surface contact the second surface of the further workpiece the shape of the working surface including the cavities receiving the displaced material of the projection has formed the material of the projection into a rosette shaped stake which positively locks the further workpiece to the plastic workpiece.
However, such a joint may be disadvantageous, because in order to positively lock the further workpiece to the plastic workpiece the rosette shaped stake projects up from the second surface of the further workpiece so that there is no smooth second surface of the further workpiece. Another drawback of the joint known in the art is that an undesirable high amount of material is necessary in order to form the rosette shaped stake, which in turn introduces undesirable additional weight for the two workpieces to be joined.
Therefore, there remains a need in the art for a method for joining a plastic workpiece to a further workpiece, wherein a safe and reliable joint is established while at the same time a possibly smooth second surface of the further workpiece is formed and as little material as possible and, thus, as little weight as possible is required for said joint.